Implantable stimulation devices of the type having electrical circuit components are well known in the medical arts. In one particularly common form, the implantable device comprises a pacemaker unit having an appropriate electrical power supply and related control circuitry for use in electrically stimulating a patient muscle, such as the heart. Such pacemaker units commonly include an hermetically sealed case or housing within which the power supply and control circuitry are protectively encased, in combination with one or more conductive pacemaker leads extending from the housing to the selected muscle structure within the patient. Feedthrough terminals on the pacemaker housing accommodate hermetically sealed passage of electrical conductors to the housing exterior for appropriate connection to the pacemaker lead or leads, typically through the use of so-called connector blocks having set screws or the like for secure lead attachment. The connector blocks and associated feedthrough conductors disposed externally of the pacemaker housing are commonly encased within an hermetically sealed head structure, such as an insulative head of cast epoxy or the like.
In the past, considerable research and development activity has focused upon the design of feedthrough terminals for permitting pacing signals to be transmitted from the hermetically sealed unit housing. Similarly, significant efforts have been directed toward the design of pacemaker lead connector blocks for obtaining a secure yet hermetically sealed electromechanical connection to pacemaker leads. However, comparatively little attention has been directed to the design of conductors and related installation methods for electromechanically interconnecting the feedthrough terminals with the associated lead connector blocks. To the contrary, available pacemaker units have predominantly utilized elongated wires extending from the feedthrough terminals and individually shaped by bending for appropriate connection by welding or the like to the associated connector blocks. Unfortunately, the close working space provided in a desirably compact implantable device makes this wire bending and shaping procedure both tedious and time consuming. Moreover, in pacemaker units having multiple feedthrough terminal conductors, significant attention and skill are required to maintain the conductor wires in sufficiently spaced array to avoid short circuit failures during pacemaker unit operation.
Recently, there have been significant improvements in devices and methods for electrically interconnecting feedthrough terminals with lead connector blocks in a heart pacemaker unit or other implantable stimulation device, particularly with respect to permitting the desired electrical interconnections to be made quickly and easily with multiple conductors arranged and maintained in spaced relation to prevent short circuit failures. Such improvements are exhibited by the commonly-assigned U.S. Pat. Nos. 5,282,841; 5,235,742; and 5,067,903 to Szyszkowski. As disclosed in those patents, a ribbon conductor set is provided for facilitated electrical connection of feedthrough terminals and lead connector blocks in an implantable stimulation device, such as a heart pacemaker unit or the like. The ribbon conductor set comprises a plurality of conductor ribbons formed as a set in predetermined number, spacing, and geometry to extend between multiple conductors at one or more feedthrough terminals and a plurality of lead connector blocks individually associated with the feedthrough conductors. The conductor ribbons are adapted for installation as a group into a pacemaker unit, and in an orientation which accommodates relatively simple connection to the feedthrough terminals and connector blocks by spot welding or the like.
The commonly used form of welding which has heretofore been satisfactory for implantable stimulation devices has been resistance welding which unfortunately is operator dependent with many variables including electrode wear, force, and voltage. The inventors and others have come to recognize that laser-welding would be desirable for joining small diameter wire to electrodes and connectors, notwithstanding the fact that resistance welders are less expensive than laser welders.
In many instances, present laser weld design concepts for joining small diameter wire (or rod) to electrodes and connectors cannot be used to reliably produce a joint. Components made from dissimilar materials having different melting temperatures, normal component fabrication variability, insignificant thermo mass inherent with certain components, imprecise component alignment during assembly, and unlike materials with distinctly different melting temperatures, are major factors that affect the reliability and repeatability of weld connections using conventional design concepts.
Typical of more recent developments in this regard is the commonly-assigned U.S. Pat. No. 5,103,818 to Maston et al. In this instance, an arrangement is provided which enables the rapid and effective termination of electrical junctions, also for an implantable stimulation device. In this instance, a circuit board supporting electronic circuitry is receivable in a housing for the medical device and is provided with a plurality of female connectors on its outer surface positioned and shaped to receive and guide male components into mating abutting engagement therewith. When the male components and the female connectors are in abutting engagement, they are fusion welded as by a laser or electron beam.